DESCRIPTION (From the Applicant's Abstract): The long-term goal of this project is to elucidate basic principles of gustatory function. A detailed analysis of the recently discovered GR family of candidate taste receptors is proposed. The proposal addresses fundamental issues of receptor function, taking advantage of the strengths of Drosophila as an experimental system. Understanding of insect taste may also be useful in controlling insect vectors of human disease, which receive gustatory cues from their human hosts. The first aim is to identify and classify all members of the OR gene family, and to characterize their genomic organization. Extant mutations affecting OR genes will be sought. The expression of GR genes will be analyzed. Initially, RT-PCR analysis will be used to determine how many family members are expressed in the taste organs of Drosophila. As a test of specificity, the taste organs of a mutant lacking chemosensory neurons will be examined, as will certain non-gustatory tissues. A major goal is to confirm and extend the results of RT-PCR analysis by other means, especially by means that indicate which cells express individual OR genes. In situ hybridization, immunohistochemistry, and reporter gene fusion experiments will be performed with a view to determining whether individual OR genes are expressed in subsets of taste neurons, whether individual taste neurons express multiple OR genes, and whether OR proteins localize to the dendrites of taste neurons, as expected of taste receptors. The hypothesis that OR proteins are in fact taste receptors will be tested directly, by analysis of two OR mutants that are already available, and of flies that overexpress individual OR genes. Responses to a panel of taste stimuli will be tested, initially by a sensitive behavioral paradigm. If mutant phenotypes are detected, they will be examined by physiological analysis of individual taste neurons, in vivo. If either the underexpression or overexpression of a GR gene produces a specific taste phenotype, then the project will provide strong evidence that GR proteins are in fact taste receptors, a ligand for a receptor will be identified, and information about the specificity of a taste receptor will be gained.